In a conventional hermetic compressor, a piston linearly reciprocates in a cylinder formed within a cylinder block to compress working fluid. The working fluid can be sucked into and discharged from the cylinder under the control of the valve apparatus.
In general, the valve apparatus is provided on a valve plate which is mounted onto a leading end of the cylinder block to close an interior of the cylinder. A flow passage is formed in the valve plate for communicating the cylinder with the outside (i.e., suction chamber and discharge chamber), and the flow passage is closed or opened by a suction valve or discharge valve. The opening and closing of the suction or discharge valve is performed by means of a difference between the cylinder pressure and the outside pressure, which results from the reciprocating motion of the piston.
Such suction or discharge valve opens and closes the flow passage at high rate during the operation of the compressor. Here, more specifically, a free-end tip portion of the suction or discharge valve opens and closes the flow passage of the valve plate. That is, the flow passage is closed when the tip portion of the suction or discharge valve comes into close contact with a valve seat of the valve plate, whereas the flow passage is opened when the tip portion of the suction or discharge valve is separated apart from the valve seat.
As described above, however, since the tip portions of the valves repeatedly strike the valve seat during the operation of the compressor so that the flow passage can be opened and closed, a large amount of noise is generated.
In the meantime, efficiency of the compressor is largely related to the valve apparatus. Energy loss in the compressor is influenced by the operation of the suction and discharge valves for opening and closing the flow passage formed in the valve plate.
As for the valve apparatus, factors having influence on the compressor efficiency include opening delay phenomena of the suction and discharge valves. One of the primary factors in such valve opening delay phenomena is inertia of the valves having various configurations and weights. The inertia is referred to as a tendency of causing the valve to maintain an original motion state. In particular, a state where the flow passage is closed by the valve is maintained at an initial stage when the valve is opened by means of the pressure difference of the working fluid from the state where the flow passage is closed by the valve, and thus, the valve opening is retarded.
The adhesive force resulting from viscous oil interposed between the valve and the valve seat of the valve plate can also cause the valve opening to be retarded. Further, inappropriate shapes of the valve seat and the flow passage formed in the valve plate can cause the opening delay phenomena to occur.